Electrical printed circuit boards (or printed wiring boards) with their mounted circuit components are well known and have long provided an advantageous technique for assembling electronic components in an orderly fashion and connecting these components together to form electronic circuits. The interconnections between these electronic components can be formed by printing or machine-depositing conductors on an insulating surface of the printed circuit board. Alternatively, the insulating surface is covered with a conductive material, the desired interconnection paths are masked, and the remaining unmasked portions of the conductive surface are etched away. The insulating layer of the printed circuit board is usually composed of phenolic-glass epoxy laminate, polyimide laminate, or ceramic. The conductive interconnecting material is usually copper.
With advances in the development of miniaturized and micro-electronic circuits for printed circuit boards, it has become necessary, and increasingly difficult, to develop interconnection techniques for accurately connecting adjacent circuit elements on a printed circuit board and interconnecting adjacent printed circuit boards. In the early 1960's the dual in-line package (DIP) became a popular package for integrated circuits. The DIP has a lead spacing of 100 mils. With increasing miniaturization and the desire to place more integrated circuits onto a circuit board, flat pack integrated circuit packages were developed and saw industry-wide use in the mid to late 1960's. Because lead spacing for flat pack packages is 50 mils, more flat pack packages than dual-in-line packages can be interconnected on a given printed circuit board. With the continued development of still smaller and more complicated integrated circuits, known as very high-speed integrated circuits (VHSIC), lead spacing has decreased to 20 mils.
As more components are mounted on a printed circuit board, it becomes necessary to provide more interconnection points between printed circuit boards of an electronic system. As is well known in the art, the typical technique for interconnecting boards is by providing a row of contacts or pins along one edge of each board such that each board (referred to as daughter board) may be plugged into a matching socket located on a mother board, establishing an interference contact. Interconnection wiring is provided between the pins on the daughter board and the daughter board electronic components, and between the socket on the mother board and the mother board electronic components. Both the contacts and sockets have to be built with care and accuracy to provide a reliable contact between the boards; the cost of providing these interconnections using the prior art methods can easily become a substantial part of the total system cost. Current interconnect requirements frequently require a connector to make 200 to 400 contacts with the contacts spaced apart by 30 to 50 mils. Using a pin-socket arrangement with this spacing, it is easy for one or more of the pins to become deflected and/or mate improperly in the socket, causing poor contact or no contact. Also, the insertion force, which is only two to four ounces per pin, aggregates to 50 to 100 pounds of insertion force in a high-pin count connector. Thus the problems caused by close connector spacing have become a dominant failure mode in electronic systems.
Alternatively, the interconnections between the mother and daugter board can be made in other ways. The connection can be made in a permanent manner using soldered or welded joints. While this provides a less costly initial assembly, it is difficult and expensive to later repair a system having permanent interconnections. Also, ribbon cables are frequently used to interconnect printed circuit boards. Each ribbon cable comprises a plurality of wires arranged side by side in a flat configuration. Each wire of the ribbon cables can be permanently soldered to a point on a printed circuit board, or connectors can be placed at one or both ends of the ribbon cable for insertion into a socket on the printed circuit boards.
Today, the principle technique for avoiding the prior art pin crunching connector mating device is to use connectors commonly referred to as the zero insertion force connectors. In this type of connector the pins and sockets are mated without any contact of the mating surfaces so that there is very little mating force. After the two halves have been mated, a latch or cam mechanism is operated to engage all of the contacts and complete the interconnection. Another advantage usually associated with zero-insertion force connectors is volume reduction over the prior art pin-socket arrangements. This feature is especially important in small-space environments, such as avionics packages for aircraft. These zero insertion force connectors have become very popular and many different types are available. Such a zero insertion force connector is disclosed and claimed in U.S. Pat. No. 4,517,625. This patent discloses and claims a circuit board with a plurality of electrical contacts mounted along an edge thereof. The housing into which the circuit board is placed has at least one zero insertion force socket including a plurality of contacts mounted therein. The circuit board is placed in the socket and a pair of jaws are moved to releasably engage the edge portion of the circuit board. With the motion of the jaws the electrical contacts of the circuit board are brought into contact with the electrical contacts on the housing.
By eliminating the pin-socket configuration, most zero insertion force connectors reduce the signal path length from the daughter board to the mother board, and also eliminate the possibility of discontinuities at the pin-socket connection. At the high frequencies associated with today's VHSIC and microwave technologies, these features reduce signal losses and delays. The present invention further improves upon these features.